Effects of permethrin at different temperatures on pyrethroid-resistant and susceptible strains of Anopheles

• Published in: Medical and veterinary entomology Vol. 13; no. 4; pp. 415 - 422
• Main Authors: Hodjati, M.H, Curtis, C.F
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01.10.1999
• Subjects: ambient temperature; Animals; Anopheles - drug effects; Anopheles gambiae; Anopheles stephensi; Culicidae; disease vectors; Dubai; Female; Freshwater; impregnated fabrics; India; insecticide resistance; insecticide treated nets; Insecticides - pharmacology; irritability; irritancy; irritant properties; Kenya; knockdown; knockdown resistance; malaria vectors; mortality; mosquito nets; Permethrin; Pyrethrins - pharmacology; pyrethroid; resistance; species differences; Tanzania; Temperature; vector control
• ISSN: 0269-283X; 1365-2915
• DOI: 10.1046/j.1365-2915.1999.00198.x

The influence of temperature (16, 22, 28, 37 degrees C) on effects of permethrin was investigated for susceptible and pyrethroid-resistant strains of the mosquitoes Anopheles gambiae and An. stephensi (Diptera: Culicidae). Young unfed female adult mosquitoes were exposed to 0.25% permethrin test papers or to polyester netting treated with permethrin 500 mg a.i./m(2). The time to 50% knock-down (KT(50)) declined as temperature increased, i.e. there was a positive temperature coefficient of this effect of the pyrethroid. Resistance ratios (comparing KT(50) values) between resistant and susceptible An. stephensi ranged between 2.5 and 4.4 at the different temperatures. Comparative tests of pyrethroid tolerance of different strains would be valid over the 22-28 degrees C range but, when using a discriminating dose to detect resistance, more precise temperature control is desirable. Mortality 24 h after exposure to 0.25% permethrin of both susceptible and resistant strains of An. stephensi showed a negative correlation with temperature between 16 and 22 degrees C and a positive correlation at higher temperatures. In An. gambiae, however, the correlation was positive over the whole range. Irritancy of permethrin-treated netting to Anopheles females (measured as time lapse until first flight take-off, and the number of take-offs during 7.5 min exposure) was positively correlated with temperature in all four strains and was much greater for the susceptible than the resistant strains.